This invention relates to circuits for electric discharge lamps and especially to circuits to be added as converter circuits to existing discharge lamp circuits to enable a different type of discharge lamp to be operated.
To conserve energy and/or to improve light output it may be desirable to replace an existing discharge lamp of a luminaire with a discharge lamp of another type. For example, in many circumstances it is desirable to replace a high pressure mercury lamp with a high pressure sodium lamp or with a low pressure sodium lamp.
It is known that such different types of discharge lamp have different electrical operating characteristics and accordingly it has hitherto been the practice when replacing a discharge lamp of one type with a discharge lamp of another type to replace the whole of the existing control gear as well as the lamp. For example, the MBF choke for an MBF lamp is, in the prior art, replaced with a leakage reactance transformer where the replacement lamp is a low pressure sodium lamp, and replaced with a combination of a suitable choke and igniter circuit for a high pressure sodium lamp. The power factor capacitor is also replaced for a high pressure sodium lamp.
It is therefore an object of the present invention to provide a means of converting an existing discharge lamp operating circuit for one type of discharge lamp to allow operation of another type of discharge lamp without replacing the existing discharge lamp operating circuit.
It is more particularly an object of the present invention to provide a converter circuit which, when added to an existing operating circuit for a mercury lamp, enables the resultant circuit to operate a sodium lamp.
It is a further object of the present invention to provide a converter circuit comprising circuit components which allow operation of a different type of discharge lamp from the type intended to be operated by an existing lamp operating circuit to which the converter circuit is added, the converter circuit also protecting the components of the existing lamp operating circuit from electrical conditions arising from operation of the discharge lamp of different type or from operation of the converter circuit.